This invention relates to a heating furnace for bringing a circulating gas stream to a very high temperature of the order of 3000.degree. K. The invention applies primarily although not exclusively to the experimental equipment units which are intended to produce molecular jets by extracting and transferring in a high vacuum the axial portion of a supersonic jet which is discharged from a nozzle, this objective being achieved by making use of suitable diaphragms (divertors, collimators) designed to separate a series of adjacent chambers in which progressively higher degrees of vacuum are obtained. In equipment units of this type, the furnace can serve to vary the gas-generating temperature within the nozzle in a continuous manner from 300.degree. to 3000.degree. K and consequently to vary the energy of the molecules forming the molecular jet in proportion to said temperature. By combining this heating effect with the aerodynamic acceleration effect which takes place naturally within a supersonic jet of a mixture containing a high proportion of a light carrier gas (hydrogen or helium), it is possible to produce molecular beams having kinetic energies in the particularly interesting range of 0.05 to 40eV, for example.
Beams having this energy are of considerable interest in the field of fundamental and applied research; this energy range in fact corresponds to the energies employed in the majority of physico-chemical processes, in excitation, ionization and dissociation processes and also in interactions between gases and solids. The furnace aforementioned can also be employed in different fields such as researches in wind tunnels, aerodynamic lasers and so forth.
In the prior art, heating of the circulating gas is produced by Joule effect through small tubular reservoirs which are usually constructed of tungsten and the side walls of which serve as heating resistors. The gas is admitted and circulates continuously within the tubes and escapes in the form of a supersonic jet through a small orifice which performs the function of a nozzle.
Devices of this type are attended by a number of disadvantages: the alignments which are essential for the formation of the molecular jet are liable to be highly disturbed by expansion effects which modify the location of the discharge orifice to the nozzle; moreover, the dimensions of said orifice cannot be modified as is occasionally necessary according to the nature of the gas without changing the entire device. It is in fact very difficult to secure a demountable component to a tungsten tube which can be machined only with difficulty by reason of the extreme brittleness of tungsten; moreover, the evacuated tubular reservoir is capable of withstanding only pressures of fairly low value, especially at high temperature. Systems of this type cannot be employed for molecular jet generators which operate with a very high generating pressure of the order of 10.sup.4 Torr.